In a high frequency signal device having an electrostatic type vibrator as a component thereof, a DC bias voltage is applied to that vibrator. In case of supplying a DC bias voltage to such an electrostatic type vibrator, if, for example, the supply thereof is carried out by using a simple transmission line, there is a fear that a voltage fluctuating in accordance with unstability of the DC feeding circuit or a high voltage generated by some factors may be applied to an electrode (so-called, drive portion or lower electrode of vibrator) driving the vibrator. In such a case, fluctuation of a vibration amplitude of the vibrator occurs and it causes fluctuation of a signal processing characteristic of a high frequency signal device. In a case when the voltage fluctuation is significant, it becomes a state in which the vibrator cannot recover caused by a phenomenon that the drive portion and the lower electrode of the vibrator are firmly fixed, discharge occurs between the drive portion and the lower electrode, abnormal vibration is generated or the like.
For example, there has been proposed a high frequency filter constituted by using a MEMS (Micro Electro Mechanical System) device, but it is difficult in such a high frequency filter to obtain a preferable filter characteristic, because time fluctuation of the vibrator impedance occurs if fluctuation of the DC bias voltage occurs. In a case when a semiconductor integrated circuit is constituted by installing the MEMS device in a digital circuit, a power supply is commonly used for a drive circuit of a digital signal processing portion and for the MEMS device and the stability thereof is not heightened particularly, so that there is a fear of characteristic fluctuation of the MEMS device caused by voltage fluctuation of the power supply. A high frequency filter utilizing a MEMS device is proposed from research institutes starting from University of Michigan (see Non-patent Document 1).
[Non-patent Document 1] C.T.-Nguyen, Micromechanical components for miniaturized low-power communications (invited plenary), proceedings, 1999 IEEE MIT-S International Microwave Symposium RF MEMS Workshop, Jun. 18, 1999, pp. 48-77.